1. Field of the Invention
A method of decreasing the global dielectric constant of an inter-level dielectric is described. More particularly, the present invention relates to the use of implants into the inter-level dielectric to decrease the global dielectric constant.
2. Description of Related Art
Semiconductor wafers are fabricated using a substrate having stacked layers, generally a first metal layer, then an inter-level dielectric (ILD) layer, then a second metal layer, etc. FIG. 1 illustrates a side cross-sectional view of a portion of a wafer having a first metal layer 10 and a second metal layer 12 separated by an ILD layer 14.
A continuous need in the manufacturing of semiconductor wafers is the reduction of the interconnect capacitance of a wafer. The capacitance of a structure may be calculated using the formula       C    =          ϵ      ⁢              A        d              ,
wherein C is the capacitance of a structure, ∈ is the dielectric constant of a material within the structure, A is the cross-sectional area of the structure, and d is the distance between the two electrodes. Thus, to achieve the goal of lowering the capacitance of a material as much as possible, the dielectric constant (∈) must also be lowered as much as possible.
Typically, the ILD layer is comprised of silicon oxide (SiO2), which has a dielectric constant of 4. The lowest dielectric constant possible is 1, which is the dielectric constant associated with an air gap (or vacuum). By merely modifying the currently used ILD layer of silicon oxide, there is consequently little need to address the integration issues, such as etchability, adhesion, etc., that arise when a new and different ILD layer, such as one fabricated from a polymer material, is used. Thus, it would be desirable to modify the ILD layer such that silicon oxide could still be used as the primary material, but the modified ILD layer would have a smaller dielectric constant than the dielectric constant of 4 associated with silicon oxide.
A method of decreasing the dielectric constant of a dielectric layer is described. First, a dielectric layer is formed on a first conductive layer. A substance is then implanted into the dielectric layer.